1. Field of the Invention
This invention relates to a system for cooling internal combustion engines, particularly to a cooling system in which the mixture ratio of the cooling water circulated through a radiator with the water circulated without passing through a radiator is controlled in accordance with the temperature of the cooling water supplied to the engine.
2. Prior Art of the Invention
In the conventional cooling system for water-cooled internal combustion engines the intercommunication between a main water line in which the water passes through a radiator and a by-pass water line in which the water circulates without passing through the radiator is controlled by a thermo-valve operated in accordance with the water temperature. Generally, a wax-type thermostat valve is used as the thermo-valve. However, the conventional controlling system using such wax-type thermo-valve has drawbacks which result from some special characters of the wax-type thermostat. Namely, since the wax-type thermostat operates responding to the meltage of wax contained therein, tne time for the response requires inevitably a somewhat long time (about 80 sec. in general). Consequently, the operation does not necessarily follow the rapid variation of conditions such as the engine load, and sometimes there are caused undesirable phenomena such as overheating at the time of going up a steep slope, a hot soak or a dead soak at the time of a sudden stop and an over-shoot at the time of a rapid start. Especially, in the running in a cold area, there occurs sometimes an over-shoot accompanied with hunting, which would shorten the life span of the engine and might cause the engine damage, unless the thermostat is replaced with a thermostat for the cold area. Furthermore, owing to the hysteresis character or the delay of response time, there comes inevitably some aberration of the temperature of cooling water, for instance, there is ordinarily an aberration of about .+-.3.degree. C. at the inlet to the engine even in a constant running condition. At the time of speed transition when the engine rotation is increasing rapidly, the thermostat is subjected to a strong fluid power and tends to over-open, which would decrease the temperature of the cooling water at the engine inlet excessively. Since the temperature for opening or closing the valve has to be fixed, it is impossible to choose an adequate water temperature according to or following the engine load, the HC amount in the exhaust gas or the fuel consumption rate. The wax contained in the thermostat, would leak out or be degraded during use. It takes often a long time to exhaust air from the valve at the time of pouring water thereinto, as the air-exhausting hole cannot but be rather small. On the contrary, the time for warming up the engine becomes long in a cold area, as the cooling water in the radiatorside often flows into the valve from the above a small airexhausting hole during engine stop.